The EPRs are elastomeric copolymers and terpolymers used in such applications as hose and tubing, wire and cable, gaskets, and single ply roofing. They are usually formulated with fillers, oils, processing aids, and stabilizing agents, and cured by reacting the polymers with sulfur in the presence of accelerators or with a combination of sulfur and an organic peroxide such as dicumyl peroxide.
These polymers are presently manufactured commercially in solution and slurry processes with soluble vanadium catalysts. These processes are very expensive to run, requiring solvent removal and steam stripping steps. In addition, these solution catalysts do not provide satisfactory particle morphology in a fluidized bed. Improvement in these processes would be desirable and, particularly, the development of a gas phase process to produce these same products would be more economically attractive because little post-reaction cost will be incurred, and particle morphology would, expectedly, be improved.
One of the catalysts selected to produce the EPRs in the gas phase is described in U.S. Pat. No. 4,508,842. Typically, the catalyst is comprised of a catalyst precursor, which is the reaction product of vanadium trichloride and an electron donor, the precursor being reacted with an aluminum containing modifier, and impregnated into a silica support; a promoter such as chloroform; and a triisobutylaluminum cocatalyst. This catalyst does achieve good particle morphology, but poor overall product, e.g., EPRs made with this catalyst exhibit poor cure and contain much high temperature crystallinity. This is believed to be the result of poorly distributed propylene, and, in the case of the EPDMs, poorly distributed diene. Adjustments with respect to the cocatalyst and the promoter were found to improve the propylene distribution and lower the high temperature crystallinity, but only a marginal improvement in the cure was achieved.